These sensors are known for their use for example as temperature or pressure sensors and generally comprise at least one resonator comprising a micro-structure deposited on the surface of a piezoelectric substrate. An exemplary sensor can typically comprise two interdigital electrode comb transducers placed between reflecting gratings. The reflecting gratings behave like mirrors and there therefore exist resonant frequencies for which the return path in the cavity is equal to an integer number of wavelengths. The resonant modes for these frequencies are excited by the transducer placed between the mirrors.
This type of sensor can be interrogated remotely, by connecting the input of the transducer to an RF radiofrequency antenna. When the antenna receives an electromagnetic signal, the latter gives rise to waves on the surface of the substrate which are themselves reconverted into electromagnetic energy on the antenna. Thus, the device consisting of an assembly of resonators connected to an antenna has a response at the resonant frequencies of the resonators that it is possible to measure remotely. Thus, remotely interrogatable sensors can be produced. This possibility is a significant advantage of surface acoustic waves and can be used notably within the framework of tire pressure sensors. It is indeed beneficial in this type of application to be able to place the sensor in the tire whereas the interrogation electronics are on board the vehicle.
According to the known art, remote interrogation systems use interrogation signals in the form of pulses (typically with a period of about 25 μs) which travel via an emitting antenna toward a receiving antenna connected to the surface wave sensor dubbed hereinafter in the description, SAW sensor.
A favored band of frequencies for systems of this type is the ISM band, the acronym standing for “Industrial, Scientific, Medical” having as central frequency a frequency of 433 megahertz and a bandwidth of 1.7 megahertz.
Generally a remotely interrogatable SAW sensor and its interrogation system can comprise, as illustrated in FIG. 1 in the simplified case of a single transducer:                an interrogation system 2;        at least one resonator 1 comprising:                    an antenna 100;            a transducer with interdigital electrode comb 11 and an SAW resonant cavity 13 characterized by its central frequency F and its quality factor Q, corresponding to the ratio between the central frequency and the passband width. The cavity 13 comprises two series of reflectors regularly spaced apart by a distance d. The transducer is connected to the antenna 100.                        
The interrogator 2 dispatches a long radiofrequency pulse to charge the resonator 1. When the emission stops, the resonator discharges on its natural resonant frequency with a time constant τ equal to Q/πF. This discharge of the resonator constitutes the return echo detected by the receiver of the interrogator. A spectral analysis thereafter makes it possible to work out the frequency of the resonator which constitutes its identification. This analysis can be performed by algorithms based on the Fourier transformation, for example of FFT type, the acronym standing for Fast Fourier Transform. This type of processing by spectral analysis is particularly complex.